Bug 1474871 - Link dump_syms against rustc-demangle. r=ted
The new version of breakpad imported in bug 1309172 doesn't demangle
rust symbols at all, contrary to before, where it tried to C++ demangle
them, which worked for many, although far from all. It however has
rust-demangle support as long as it's linked against a copy of the
rust-demangle-capi crate from https://github.com/luser/rust-demangle-capi/
This imports the code from the rust-demangle-capi crate but because of
some build system complications it's not taken as-is:
- it uses rusty-cheddar, which is deprecated, to generate a C header.
- rusty-cheddar depends on syntex_syntax, which now fails to build.
- rust-demangle-capi has crate-type staticlib, which can't be used
as a dependency in a Cargo.toml. For that reason, we can't create
a fake crate that depends on it to have it vendored.
Overall, it's only a few lines of rust, and the C header can be written
manually, so this is what we do here. The created crate is named in a way
specific to dump_syms.
The build system doesn't know how to figure out what system libraries
are required to link rust static libraries, although the rust compiler
has /some/ support to get the information, so we handle that manually.

[workspace]# These are the "root" crates, which we build and test as top-level targets.# Their transitive dependencies and dev-dependencies are included automatically# and do not need to be listed here. Their external dependencies are vendored# into `third_party/rust` by `mach vendor rust`.members = [ "js/src", "js/rust", "js/src/frontend/binsource", # Code generator. "testing/geckodriver", "toolkit/crashreporter/rust", "toolkit/library/gtest/rust", "toolkit/library/rust/",]# Excluded crates may be built as dependencies, but won't be considered members# of the workspace and their dev-dependencies won't be included.exclude = [ # Exclude third-party code vendored into mozilla-central. "gfx/webrender", "gfx/webrender_api", "gfx/webrender_bindings", "servo", "third_party/rust", # Excluded because this is a standalone tool for developers and not intended # to be built as part of mozilla-central and is not shipped to users. "gfx/wrench", # Excluded because these crates have their own Cargo workspaces so they can't # be included in the top-level one. "media/audioipc", "media/cubeb-rs", # Excluded because they are used only as dependencies, not top-level targets, # so we don't need to vendor their dev-dependencies. "dom/webauthn/u2f-hid-rs", "media/mp4parse-rust/mp4parse", "media/mp4parse-rust/mp4parse_capi", "media/mp4parse-rust/mp4parse_fallible",]# Explicitly specify what our profiles use. The opt-level setting here is# a total fiction; see the setup of MOZ_RUST_DEFAULT_FLAGS for what the# opt-level setting will be as a result of various other configure flags.[profile.dev]opt-level = 1rpath = falselto = falsedebug-assertions = truepanic = "abort"[profile.release]opt-level = 2rpath = falsedebug-assertions = falsepanic = "abort"codegen-units = 1[patch.crates-io]libudev-sys = { path = "dom/webauthn/libudev-sys" }serde_derive = { git = "https://github.com/servo/serde", branch = "deserialize_from_enums8" }